This study will evaluate the safety and efficacy of gene therapy in cystic fibrosis (CF) utilizing a replication deficient recombinant adenovirus (Av1Cf2). Av1Cf2 will be used to deliver the human cystic fibrosis transmembrane conductance regulator (CFTR) cDNA to the upper respiratory tract of cystic fibrosis patients. Fifteen subjects will be studied in groups of three. Each group will receive an escalating dose of Av1Cf2 starting at 1x10(6) pfu and increasing by half-log increments after acute toxicity studies verify the safety of the regimen. Safety, gene expression, and antibody response will be evaluated.